The present invention relates to punches and apparatus for perforating film material such as polyethylene film or other films made of plastic resin. The invention is more particularly directed to an improved slitter-punch and adapter combination for such apparatus in which the slitter blade and hole punch are formed as a unit, and can be changed out quickly and replaced with a minimum of machine down time.
Currently, blades and cutters for forming holes and slits in plastic film material are separately provided. For example, in my prior U.S. Pat. Nos. 4,748,920 and 4,723,466, apparatus are described for punching holes in plastic film material and also cutting a tear slit in the material. In that case there is a self-sharpening hole punch formed of a low-friction, semi-rigid material, such as Delrin or a similar polymer. The hole punch has a thread at its upper end for screw mounting onto reciprocating apparatus, which may be actuated by a pneumatic cylinder. Slit cutters are separately mounted on the reciprocating mechanism and spaced a small distance from the hole punch to create a gap in the film between the resulting hole and slit.
A so-called quick-slip punch adapter for a plastic bag making machine is described in U.S. Pat. Nos. 5,035,165 and 5,114,394. In that arrangement, a slitter blade is held in a clamp that also fastens to the shaft or rod that holds a hole cutter. However, the slitter blade is a separate element and has to be changed out separately from the hole punch. Also, this requires the operator to employ tools to remove the worn blades and punches, and to replace them with fresh ones. This operation can take several minutes for each hole punch and slitter blade. As there are several of these on each bag machine, considerable down time may be required to replace the worn blades and cutters.
Also, when the space between the slitter blade and the hole punch is to be changed, this must be done by hand and the gap between the slitter and the hole punch must be carefully measured. Moreover, the slitter blade itself has always been made of steel, and suffers the problems of dulling and wear that characterize steel cutting heads, which problem is discussed in the above-mentioned U.S. Pat. Nos. 4,748,920 and 4,723,466. Consequetly, the industry has long sought a solution to the problem of how to effect rapid change out of both hole punch and slitter blade, how to effect proper alignment of the parts in the desired spacing, and how to increase the wear life of the parts.